/*
 * @lc app=leetcode.cn id=21 lang=csharp
 *
 * [21] 合并两个有序链表
 */

// @lc code=start
/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int val=0, ListNode next=null) {
 *         this.val = val;
 *         this.next = next;
 *     }
 * }
 */
public class Solution {
    public ListNode MergeTwoLists(ListNode list1, ListNode list2) {
        if(list1 == null)
            return list2;
        if(list2 == null)
            return list1;
        
        ListNode head = new ListNode();
        ListNode cur = head;
        while(list1 != null && list2 != null)
        {
            if(list1.val < list2.val)
            {
                cur.next = list1;
                list1 = list1.next;
            }
            else
            {
                cur.next = list2;
                list2 = list2.next;
            }
            cur = cur.next;
        }
        cur.next = list1 != null ? list1 : list2;
        return head.next;
    }
}
// @lc code=end

